New energy vehicles are widely promoted in China and the world, but there are still many improvements that need to be made to completely replace fuel vehicles. For example, problems that a mileage of a car is small, a cost of a battery pack is high, and a reliability of the battery pack is low and the like need to be further solved. Based on the above problems, higher requirements are imposed on a secondary battery, i.e., the core part, of an electric vehicle, for example, the secondary battery is required to achieve higher energy density, lower cost, and the like.
At present, the secondary battery generally adopts a square hard housing structure, and the secondary battery housing includes a casing and a cap assembly, and the secondary battery housing provides a sealed space for accommodating an electrode assembly and electrolyte. The electric energy of the electrode assembly is introduced from the sealed space to the outside of the sealed space through an electrode terminal of the cap assembly. In the existing cap assembly, the cap plate is a metal plate and is provided with a through hole, the electrode terminal is divided into a base portion and an extension portion, and a cross-sectional area of the base portion is larger than a diameter of the through hole. During assembly, the base portion is located below the cap plate (i.e., inside the casing), and the extension portion is fixed by a circlip or by riveting after the extension portion passing through the through hole. In this way, the electrode terminal is fixed to the cap plate. Since the base portion is located inside the casing, a space utilization inside the casing is low, thereby reducing an energy density of the secondary battery.
Due to the structure of the electrode terminal itself and the complicated assembly process, not only the assembly efficiency of the secondary battery is affected, but after the electrode terminal is fixed on the cap plate, the electrode terminal and the cap plate are often disconnected due to insufficient fixing force, thereby reducing reliability of use of the secondary battery.